On Sep 15, 2008, at 10:00 PM, Rockson Li (zhengyli) wrote: > check RFC3261 sec 13.3.1.4 > > Since 2xx is retransmitted end-to-end, there may be hops between > UAS and UAC that are UDP. To ensure reliable delivery across > these hops, the response is retransmitted periodically even if > the > transport at the UAS is reliable. > > Even more critically, there may be insane or overloaded proxies in the path that drop or defer the message. So even if TCP is used end-to- end, SIP requires retransmission-until-acknowledgement at the protocol level. I have long maintained that if we'd thought this through that instead of the three-message INVITE transaction that we'd have been better off using opposing pairs of two-message transactions. Carrying payloads in what are essentially acknowledgement messages (200) was a bad idea. But it's what we do, hence the retransmission. -- Dean _______________________________________________ Sip mailing list https://www.ietf.org/mailman/listinfo/sip This list is for NEW development of the core SIP Protocol Use [EMAIL PROTECTED] for questions on current sip Use [EMAIL PROTECTED] for new developments on the application of sip
